BARRE — The Department of Fish and Wildlife is warning Vermonters about letting their cats outside.

The department says a new study from the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service has raised concerns about the welfare of Vermont’s wildlife populations. The study says cats are the single greatest cause of human-caused mortality to birds and mammals, killing around 2.4 billion birds and 12.3 billion mammals each year in the U.S.

“Cats pose a threat to Vermont’s songbirds, such as robins, bluebirds and cardinals,” said Vermont Fish and Wildlife bird biologist John Buck in a statement from the department. “Cats may even restrict the statewide recovery of some rare birds. The whippoorwill, which is a state threatened species, can easily fall prey to roaming cats during their nesting season.”

The department said cats can also lower the populations of other animals such as ducks and rabbits. Biologists in the north central part of the country post fences around duck nesting areas to keep cats and other predators out.

“This is more of a pervasive problem for wildlife than many people realize,” said Fish and Wildlife biologist Steve Parren in the statement. “It was a wakeup call for my family when our friendly tabby delivered a still struggling baby bunny to our doorstep. We realized the potential consequences of allowing our cat to roam outdoors.”